Within the field of pressure sensing devices, there exists a need for devices which reliably convert sensed pressures of a medium into electrical signals. Commonly such devices use piezo-resistive pressure cells which employ resistive membranes across a pressurized medium. As plastic elongation of the membrane occurs under pressure, the measured resistance yields signals correlating to predetermined pressures. However, a particular problem occurs when the device is subjected to thermal cycling, such as in hostile environments. This frequently results in thermal cycling induced expansion of the material which the device is constructed of imparting false pressure signals to the resistive membrane. In other words, the ambient thermal cycling causes mechanical elongation of the sensing membrane which then generates a false electrical signal.
Yet another problem occurs in pressure sensing devices due to the complex construction of these devices. Some pressure sensing structures consist of many fittings and require bonding of leads between fittings. Other devices may require crimping or movement of threaded sleeves in order to join the various parts or fittings to form a complete device. These structures are often expensive to manufacture due to the many steps involved in assembly.
What has been needed, therefore, is a pressure sensing device which accurately senses pressure of a pressurized medium and converts the sensed pressure to an electrical signal which is independent of ambient thermal cycling which the pressure sensing device is exposed to.
What has been further needed is a simply constructed pressure sensing device which provides reusable and snap-fit attachment of a cap member to a body member so that electrical connections are achieved during assembly independent of any lead bonding requirement.
Other objects and advantages will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein are set forth by way of illustration and example certain embodiments of the present invention.